Towards Naked Zinc(II) in the Condensed Phase: A Highly Lewis Acidic Zn^II Dication Stabilized by Weakly Coordinating Carborate Anions

Abstract

The employment of the hexyl-substituted anion [HexCB 11 Cl 11 ] À allowed the synthesis of a Zn II species, Zn[HexCB 11 Cl 11 ] 2 , 3, in which the Zn 2+ cation is only weakly coordinated to two carborate counterions and that is soluble in low polarity organic solvents such as bromobenzene. DOSY NMR studies show the facile displacement of at least one of the counterions, and this near nakedness of the cation results in high catalytic activity in the hydrosilylation of 1-hexene and 1methyl-1cyclohexene. Fluoride ion affinity (FIA) calculations reveal a solution Lewis acidity of 3 (FIA = 262.1 kJ mol À1) that is higher than that of the landmark Lewis acid B(C 6 F 5) 3 (FIA = 220.5 kJ mol À1). This high Lewis acidity leads to a high activity in catalytic CO 2 and Ph 2 CO reduction by Et 3 SiH and hydrogenation of 1,1-diphenylethylene using 1,4-cyclohexadiene as the hydrogen source. Compound 3 was characterized by multinuclear NMR spectroscopy, mass spectrometry, single crystal X-ray diffraction, and DFT studies.

Synthesis, Reactivity, and Lewis Acidity of Cationic Zinc Complexes

“…However, the coordination of Lewis bases to such species or replacement of the alkyl substituents by sterically more demanding chelating substituents allowed the isolation of several cationic zinc complexes and their structural characterization, − respectively (Scheme ). Despite the increased coordination number and reduced electrophilicity of these complexes in comparison to alkyl-substituted derivatives, many of them are still strongly Lewis acidic and were successfully applied in catalytic reactions. , Complexes I and VI were even found to reduce CO 2 to CH 4 quantitatively in the presence of Et 3 SiH, , whereas complex X is active in the ROP of lactide …”

“…Despite the increased coordination number and reduced electrophilicity of these complexes in comparison to alkyl-substituted derivatives, many of them are still strongly Lewis acidic and were successfully applied in catalytic reactions. 20,21 Complexes I and VI were even found to reduce CO 2 to CH 4 quantitatively in the presence of Et 3 SiH, 22,23 whereas complex X is active in the ROP of lactide. 13 Monoanionic β-diketiminate ligands ( R nac 2 − ) have become very popular for the stabilization of low-coordinate maingroup-metal and transition-metal complexes, including lowvalent and cationic complexes, in the last decades.…”

A Single Bioinspired Hexameric Nickel Catechol–Alloxazine Catalyst Combines Metal and Radical Mechanisms for Alkene Hydrosilylation

“…the same hydrodynamic volume [67] . A dynamic behavior of a complex in solution may thus be evidenced by changes in hydrodynamic volume and diffusion coefficient (D) [68,69] . DOSY experiments were performed first in d 6 ‐DMSO where both ligand and complex are soluble.…”

Chiral Tetra-coordinate Aluminum Cation in Catalysis

“…To quantify the Lewis acidity of [ 3 ] + , the solvation corrected fluoride ion affinity (FIA) of [ 3 ] + , BCF, Al­(C 6 F 5 ) 3 , Al­(OC­(CF 3 ) 3 ) 3 , and SbF 5 was computed with the BP86-D3­(BJ) method and def2-SVP basis set with the conductor-like polarizable continuum model (CPCM) for DCM solvation. , As summarized in Table S3, [ 3 ] + (480 kJ/mol) displays higher affinity toward fluoride than BCF (409 kJ/mol), which is consistent with the base competition experiment. With an FIA value comparable to that of SbF 5 (489 kJ/mol), Al­(C 6 F 5 ) 3 (493 kJ/mol), and Al­(OC­(CF 3 ) 3 ) 3 (503 kJ/mol), we can conclude that [ 3 ] + is indeed a strong Lewis acid.…”